turn west of the inlet. Backpassing to the east of the relocated inlet will likely not be necessary
because of impoundment at the east jetty and gradual increase in width of the eastern beaches.
Table 1. Regional Sediment Management Issue and possible performance of alternative.
Sediment Management Issue
Existing Inlet performance
Relocated Inlet performance
Expected to perform similarly as other LI
inlets, and at much reduced cost as
Relatively difficult and costly as
1. Navigation channel reliability
compared to other LI inlets
compared to present
Erosion threat at Gilgo Beach and
Eliminates erosion at Gilgo Beach and
2. Erosion at Gilgo Beach and
western beaches continues, butis
westward beaches for ~ 50-100 years
reduced by periodic bypassing of
through collapse of existing ebb shoal and
westward beaches, with road
endangered during storm
dredged sand
building of wide beaches
Likely not necessary for many years west
of inlet; east of inlet, between old jetty and
new west jetty, monitor and bypass as
necessary. Probably best not to allow
3. Sand bypassing
new inlet east jetty fully impound bypass
accompanying dredging
from the impoundment fillet.
Continue existing practice
4. Erosion, strong current, and
possible wave action along Oak
Erosion, strong current, and direct wave
Island Beach
Erosion threat continues
impact eliminated
5. Erosion on beaches to east
Erosion threat continues, reduced by
Impoundment at east jetty will create wider
of Fire Island Inlet
occasional sand backpassing
beaches to east
Dependent on state and local
decisions
6. Maintenance of sand dike
No longer necessary
Bayside erosion possible at ends of new
jetties; protective measures need to be
7. Erosion on back (northwest)
Monitor existing revetment
incorporated in design
side of Democrat Point
Will likely not be greater than existing
condition for slow-moving northeasters,
but surge may rise more rapidly for fast-
moving tropical storms. Needs to be
calculated for quantification. The
relocated inlet would release bay waters to
8. Storm surge in Great South
No change
the ocean more rapidly than existing inlet
Bay
Will increase tidal range; preliminary
calculations show the lows to become
lower, not the highs to become notably
higher, but more accurate calculations are
9. Increased tidal range in
necessary. The relocated inlet would
Great South Bay
improve circulation in Great South Bay
No change
No change of tendency for flood
New flood shoal would form, covering
10. Formation of flood shoal
shoal growth off Oak Beach
existing bay bottom.
Development of Ebb and Flood Shoals at Relocated Inlet
The volume of the flood shoal that will form at the relocated inlet can be estimated by an
empirical predictive formula found by Carr de Betts (1999) in terms of the tidal prism, giving
4.6 x 106 m3, about 25% larger than the flood shoal at Shinnecock Inlet. The Reservoir Model
(Kraus 2000) allows estimation of the time history of re-establishment of natural bypassing and
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